Prefer ATTR_ in shared codebase over AT_

An earlier commit introduces AT_MODE into the shared kernel sources,
instead of the preferred existing ATTR_MODE use.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Signed-off-by: Jorgen lundman <lundman@lundman.net>
Closes #13293